1. Field of the Invention
The present invention relates to an SMPS protection circuit in an electronic appliance.
2. Description of the Related Art
The following is a description of an SMPS protection circuit in an electronic appliance according to the conventional technology made with reference to the accompanying drawings.
FIG. 1 is a block diagram illustrating a construction of the SMPS protection circuit in an electronic appliance according to the conventional technology.
As shown in FIG. 1, the SMPS protection circuit in an electronic appliance according to the conventional technology comprises an AC generating Section 10 for generating an AC voltage, an AC rectifying section 11 for receiving the AC voltage generated from the AC Generating Section 10 and rectifying the AC voltage into a DC voltage, an SMPS transformer 12 for receiving the DC voltage rectified by the AC rectifying section 11 at a primary winding and inducing a voltage proportional to the number of turns of the primary winding with respect to the corresponding secondary winding, a power supply section 16 for receiving the AC voltage generated from the AC Generating Section 10 and converting the same to DC voltage to supply as a power source, a pulse generating section 17 operated by the voltage supplied from the power supply section 16 to generate pulses of a predetermined frequency, a frequency oscillating section 15 for providing a time constant for setting the frequency of the pulse generating section 17, a switching section for switching an input power source at the primary winding of the SMPS transformer 12, an output rectifying section 13 for rectifying the voltage induced to the secondary winding of the SMPS transformer 12 into a DC voltage in accordance with an operation of the switching section 18, and a load 14.
The following is a detailed description of an operation of the conventional SMPS protection circuit in an electronic appliance constructed as above.
As shown in FIG. 1, the AC rectifying section 11 receives the DC voltage generated from the AC Generating Section 10, and rectifies the same into a DC voltage so as to be transmitted to the SMPS transformer 12. The power supply section 16 converts the AC voltage generated from the AC Generating Section 10 to a DC voltage so as to be applied as a driving voltage of the pulse generating section 17. Subsequently, the pulse generating section 17 generates pulses of a predetermined frequency, and transmits the same to the switching section 18. The switching section 18 switches the DC power source applied to the primary winding of the SMPS transformer 12 in accordance with the pulses provided by the pulse generating section 17. Thereafter, an output rectifying section 13 rectifies an output from the secondary winding of the SMPS transformer 12 into the DC voltage. The rectified DC voltage is applied to the load 14. Here, the current generated through the load 14, i.e., the load current, is variable depending on a level of the load 14.
However, the conventional SMPS protection circuit operates irrespective of variation of the load current. As a consequence, electric power is unnecessarily consumed when the load 14 is light, while the SMPS protection circuit is damaged when the load 14 is excessive.
It is, therefore, an object of the present invention to provide an SMPS protection circuit that can prevent unnecessary electric power consumption and damage of itself by controlling the power source supplied to the SMPS transformer in accordance with the load on the SMPS protection circuit.
To achieve the above object, there is provided an SMPS protection circuit comprising: a power supply section for receiving and converting an AC voltage to a driving voltage, and outputting the same; a pulse generating section for receiving the driving voltage outputted by the power supply section to generate pulses of a predetermined frequency; a frequency oscillating section for providing a time constant to set the frequency of the pulses of the pulse generating section; an SMPS transformer having a primary winding for applying an input DC power source thereto, and a secondary winding for applying an AC power source thereto; a switching section for switching the DC voltage inputted to the primary winding in accordance with the pulses generated from the pulse generating section; an output rectifying section for rectifying the output DC power source of the SMPS transformer, and supplying the same to a load; an output current detecting section for outputting a predetermined signal corresponding to a difference between the DC power source outputted by the output rectifying section and the voltage descended due to the load; an output current feedback section for outputting a voltage corresponding to the predetermined signal outputted by the output current detecting section; a frequency down section for reducing the output power source of the SMPS transformer by downing the frequency of the output pulses from the pulse generating section through variation of the time constant of the frequency oscillating section, if the voltage outputted by the output current feedback section is within a first set voltage range representing that the voltage outputted by the output current feedback section is a light load region; and a power intercepting section connected between an output terminal of the driving voltage of the power supply section and the pulse generating section for ceasing operation of the SMPS transformer by ceasing operation of the pulse generating section.